1. Technical Field
This invention relates to light weight abrasive tumbling media for use in mass industrial finishing operations and to methods of making same. More particularly, this invention relates to the production of ceramic tumbling media consisting of discrete abrasive particles of essentially uniform size and shape which exhibit a final bulk density after firing below 65 lbs/ft.sup.3.
2. State of the Art
Abrasive tumbling media have long been used in mass industrial finishing operations for refining the surfaces of metallic and plastic parts. Such media have customarily included discrete abrasive particles of various sizes and shapes made from ceramics, porcelains, natural or synthetic stone, clay, and plastics. Conventional ceramic tumbling media exhibit a bulk density of 80 to 120 lbs/ft.sup.3 which can damage delicate parts during mass finishing operations. Plastic tumbling media having a significantly lower bulk density have commonly been used for such operations, but plastic gives off an undesirable effluent during production which is harmful to the environment and which may require treatment as a hazardous waste. Accordingly, there exists a need for improved light weight, low density ceramic tumbling media the production or use of which is not detrimental to the environment.
Therefore, it is an object of the present invention to provide improved low density ceramic tumbling media suitable for refining or finishing delicate industrial parts.
It is a further object of this invention to provide improved low density abrasive tumbling media having a final fired bulk density below 65 lbs/ft.sup.3.
It is still a further object of the invention to provide light weight ceramic tumbling media, the production or use of which is not detrimental to the environment.
These and other objects are accomplished herein by adding at least 15%, and preferably 20% by weight of a naturally occurring or synthetically produced metallic carbonate to a ceramic/clay based formable mixture normally used in making conventional abrasive particles. Examples of such carbonates include calcium carbonate, lithium carbonate, magnesium carbonate, zinc carbonate or compositions containing a predominant amount of one or more of these carbonates. The carbonate is added to the mixture prior to formation. Once formed, the particles are fired at temperatures in the range of 1130.degree. C. to 1150.degree. C. to produce finished discrete particles desirably having an essentially uniform size and shape which exhibit a final bulk density below 65 lbs/ft.sup.3. The carbonate undergoes decomposition at customary firing temperatures leaving fine pores in the media which accounts for the lowering of the bulk density.